Actuation drive coils are used in a plethora of devices for precise mechanical positioning of parts. One area where actuation drive coils have found particular use is in magnetic storage drives. For example, actuation drive coils are used to align magnetic heads with data tracks on magnetic media. The recording and reading of data in tracks on magnetic storage media requires precise positioning of magnetic read/write heads. The read/write heads must be quickly moved to, and maintained centered over, particular data tracks as recording and reading of data takes place. The magnetic heads can record and read data as relative movement occurs between the heads and the magnetic storage media in a transducing direction. The heads are moved from track to track across the width of the tracks in a translating direction, which is perpendicular to the transducing direction.
For example, a recordable disk typically contains concentric data tracks and is rotated beneath a magnetic head. The direction of rotation defines the transducing direction. Radial movement from track to track defines the translating direction. A magnetic tape typically contains data tracks that extend along the length of the tape, parallel to the tape edges, in the transducing direction. In magnetic tape helical scan systems, however, the tape is moved beneath heads that are moved at an angle across the width of the tape, the diagonal direction defining the transducing direction.
Storage devices that read and record data on magnetic media typically use servo control systems to properly position the data heads in the translating direction. The servo control systems derive a position signal from a servo magnetic head that reads servo control information recorded in servo tracks on the storage media. In a timing based servo system timing information in the servo track allows the servo reader to precisely determine its' position in the servo track, and since the servo reader is a precise distance from the data writers and data readers in the recording head, locating the servo reader in the desired position in the servo track also locates the data readers and writers in their desired position.
To correctly position a tape head, for example, with respect to servo data, every tape head has an actuator to dynamically position the head in the tape drive. To explain this actuator, FIG. 1 is a simplified drawing of an actuator 100. This actuator 100 is an electromotive actuator which uses the current in coil 102 to interact with the magnetic field produced by permanent magnet 104 and produce a force on the coil. The actuator 100 also has a spring 106 which returns the head to its zero position. As shown in FIG. 2, to reduce the oscillation of the head back and forth upon changing position, damping 108 can be added to the actuator.
When building tape and hard disk drive systems that include coil actuators, it is not uncommon for one supplier to create the actuation coil, a different supplier creates the magnet, a third supplier creates the biasing spring, and yet a fourth party assembles all of the parts to create the coil actuation drive mechanism. However, because no one single party is responsible for quality control over manufacture of all of the parts, the physical characteristics of the parts may vary from lot to lot. The result is that the resonance frequency (and damping if present) may not always function within design tolerances. For instance, if the biasing strength of the spring changes, the resonance frequency will change. Similarly, if the damping gel or oil is thinner in one lot, more oscillation will be observed.
Thus, it is often necessary to measure the resonant frequency and damping characteristic of a tape had actuation drive coil in order to disposition or monitor the proper functioning of such drive coil. A quick, accurate, and inexpensive method is required for such measurements to make such measurement feasible in a manufacturing process.
One known solution is to drive the coil of the actuator with an external signal of known frequency and amplitude while simultaneously measuring the displacement amplitude response of the actuator. Several drawbacks to this technique include requiring a procedure to measure the drive amplitude and a procedure to measure the head displacement in a non-intrusive method. These methods are often costly, time intensive, and sometimes unreliable.
Therefore, a need exists for testing assembled coil actuation drives to ensure that they operate within design tolerances. A need also exists for a system and method for determining whether the quality of the parts used to create such coil actuation drives meets design parameters.